Regulating device for vacuum pumps



Patented June 23, 1936 PATENT OFFICE BEGULATING DEVICE FOR VACUUM PUMPSGeorge H. Woodard, Phillipsburg, N. J., assignor to Ingersoll-BandCompany, Jersey City, N. J., a corporation of New Jersey ApplicationJune 1, 1934, Serial No. 728,491

This invention relates to pumps, and especially to a regulating deviceto be connected to pumps for exhausting an enclosed space to establish avacuum therein. 5 An object of the invention is to provide a pump whichwill not require a disproportionatelylarge 'quantity of power to operateit when the work of creating the vacuum is first commenced.

When a vacuum pump, particularly of the ro- 10 tary type, is connected,for example, to a closed vessel, such as a condenser in which steam orother vapor is to be liquefied, so as to put the condenser ,intocondition for use by drawing out the I contained air, the pump must do agreat deal 15 more work at the start, or in the pumping up period, thanlater, when the required vacuum, which may be as high as 29 inches ofmercury, has once been set up and requires only to be maintained orcontinued. In some cases more than 20 four times as much power isnecessary at the beginning or the operation than is needed when thevacuum has once been obtained. The cause, naturally, is the fact thatatthe outset the suction pressure is higher and a greater mass of air 25has to be removed from the condenser or other vessel that is beingevacuated.

In the preferred form of my invention the pump is of the rotary vanetype, and the end is gained preferably by regulating the intake of thepump. This isdone by means of a bleeder connection to the main casing ofthe pump adjacent the outlet thereof, but which does not communicatewith the outlet and a device controlled by said connection and soarranged that the quan- 35 tity of air taken in by the pump through theinlet depends on the absolute pressure in the pump as the work ofevacuation proceeds. Thus the power to actuate the pump when theoperation commences is greatly reduced.

40 The nature and advantages of the invention are fully set forth in thedescription and drawing and the novel characteristics are defined in theclaims appended hereto, but I of course reserve the right to makechanges, not shown herein, but

45 of such a character as to be in accordance with the spirit and scopeof the invention.

On the drawing the figure shows partly in section a constructionaccording to my invention.

The numeral l indicates the cylinder or casing and a substantiallyconstant open outlet 8, leading to a discharge pipe 9. The pumppreferably discharges through the pipe 9 into the atmosphere or someother medium at constant pressure.

The working space [0 on the inside of the pump between the rotor and thecasing is crescentshaped, so that the medium entering the pump firstexpands as it is admitted through the inlet 1 and is then compressed asit is expelled through the outlet 8.

This type of pump for vacuum service usually has the disadvantage thatthe openingpf the cylinder l to the outlet is timed by the passage ofthe vanes 3 over the outlet 8. When this outlet port- 8 is located witha view to giving the best performance for creating a high vacuum in thecondenser, which of course will be connected to the inlet 1, the pumpwill at first compress to a pressure much above atmospheric, say 30 to60 pounds per square inch gauge, with low vacuum or nearly atmosphericpressure at the suction or inlet port I. As the exhaustion of thecondenser proceeds the compression pressure will drop of course, but theratio between the suction pressure and discharge pressure tends to beconstant regardless of the vacuum. Hence an excessively higherhorsepower is required when the pump begins its work to reduceatmospheric pressure in the space that is being exhausted and bring itdown to the point required. After the vacuum is established, of coursemuch less horsepower is necessary. For example, in one case 'about 8horsepower was found enough to maintaina vacuum of 29 inches, but toestablish this vacuum, a peak of about horsepower was reached during 35the initial pumping period.

My invention eliminates this peak and enables the vacuum to be obtainedby the expenditure of a reasonably uniform amount of power in the entireoperation from the start until the vacuum 40 is fully created. Toaccomplish this, I provide the cylinder l with a port ll just in advanceof the outlet opening 8, and from this port extends a conduit I! to achamber l3, in which is a diaphragm It. To this diaphragm is connected arod [5. Movement of the diaphragm and rod is opposed by a spring IS in apart of the chamber IS. The rod I5 is connected by suitable means, suchas a lever l1 and a link l8 to the arm I9 of rotary valve 20. This valveis in the intake or suction conduit 2| connecting the condenser to theinlet 1. The parts are so arranged that the spring I6 tends to open thevalveand pressure on the diaphragm tends to close it. At the point wherethe port II is located, substantially the highest compression pressuresare produced when the pump is started and the conis being pumped out,and as the maximum pressure in the casing or cylinder I drops. In otherwords, the quantity of air drawn into the pump is so restricted andregulated that the highest pressure in the casing I can never exceed thefigure selected and the valve 20 remain open. Therefore, the pump does.not impel so great a mass of air through the outlet 8 at the start andthe condenser is exhausted virtually as quickly as it would beotherwise, but very little increase in power over the amount requiredfor normal operation-is taken by the pump when the operation ofexhausting the condenser commences. The work to be done by the pump isthus more advantageously performed and the heavy initial load isobviated.

Since the pressure in the discharge pipe 9 is generallythe same asatmospheric, the pipe I2 must communicate with the interior of the pumpat some point other than the outlet 8. For that reason the pipe I2 isconnected to the port II so that the pressure upon the diaphragm I Avaries according to an intermediate pressure within the pump. Port I Iis in advance of the outlet 8 and cannot communicate with the outletbecause of the spaced relationship of the vanes 3. If this pipe I2 wereconnected to the discharge pipe 9 and if the outlet pressure wereconstant, the diaphragm I4 would always remain in one position and thevalve 20 would never be opened to a greater extent as the operationproceeds.

The purpose of the invention is thus obtained without waste of power andwithout any complicated structure being added to the pump and itsconnections. The regulating device comprising the valve and the chamberwith the conduit I2 is quite certain in operation and inexpensive toconstruct and very easy to mount in operative position.

If desired, the conduit leading to the inlet I may have a valved by-pass22 around the valve 20. This by-pass may be opened and closed by a valve23 having an outside operating knob on the stem thereof. A compressor ofthis general design is inherently a constant compression ratio machine,and at the start when pressure in the pipe I9 is at least equal to theatmosphere, the compression pressure of the pump discharging through theoutlet 8 is comparatively high. But as the exhaustion of the space wherethe vacuum is to be created proceeds, the compression pressure at boththe port II and the outlet port 8 likewise will not be so great.Therefore the valve 20 is now more and more fully opened and the volumepassing the valve 20 increases. Consequently the pressure at the portII, although it also drops somewhat to let the valve 20 be opened moreby the spring I6, also does not fall so much, and practically nopulsations or fluctuations in the power to drive the pump occur. Thismode of operation begins as soon as the pump starts and the heavyconsumption of power heretofore necessary when the work of creating thevacuum commences is eliminated. After the vacuum is produced, power isof course still required to maintain it. This power is not much lessthan at first, and the power expenditure is virtually constant, for theinitial expenditure is not much greater than what is necessary to keepthe vacuum at the desired figure. 5 In other words, the dischargepressure at the outlet 8 does not go above eight pounds by the gauge andfrom this point it falls as the work of the evacuation proceeds and thevalve 20 opens further. The distance between the port 8 and the passageII is of course slightly greater than that between any two vanes, whichare preferably located at equi-distant points around the rotor 2. Hencethe port 8 and passage II- never communicate with each other, becausejust before one of the vanes passes the outlet 8, the motion of therotor being anticlockwise, the next vane behind passes the port II andthe compressed air in the movable compression chamber or portion oi. thespace I0 between said two 2 vanes will immediately discharge through theoutlet 8, while the diaphragm ll will be subjected to the pressure ofthe next compression chamber. Some fluctuation of pressure in thediaphragm casing I3 may occur, because the 25 pressure in the nextcompression chamber increases as that chamber passes the port or passageII, but this fluctuation is so slight that it does not impair thedesired mode of operation or prevent the desired result.

I claim:

1. A vacuum pump having inlet and outlet openings and an intermediateport between the openings and incommunicable with the outlet opening, aconduit leading from a source of fluid medium to the inlet opening,means in the conduit between said source and inlet for controlling thepump intake pressure, and a device for operating said means in responseto the pressure of the fluid medium at said intermediate port.

2. A vacuum pump having inlet and outlet openings, a conduit leadingfrom a source of fluid to the inlet opening, a pressure-responsivedevice controlled by a pump pressure intermediate the inlet and outletpump pressures, said intermediate pressure being uninfluenced by thepump outlet pressure, and means operatively connected to said device foreifecting a desired restriction to the flow of fluid through saidconduit and for decreasing said restriction as said intermediatepressure decreases.

3. A vacuum pump having inlet and outlet openings and an intermediateport between said openings but not communicable with the outlet opening,a conduit leading from a source of fluid to the inlet opening, a valvein the conduit for controlling the pressure of the fluid at the pumpinlet, a duct connected to said intermediate port, andpressure-responsive means operatively connected to the valve and actingto move the valve to open position only at pressures lower than apredetermined pressure of the fluid in said duct.

4. A vacuum pump comprising a casing having an inlet and outlet openingand an intermediate 65 port, a rotor within the casing, said rotorhaving a plurality of impellers spaced around its periphery, the spacedrelationship of said impellers rendering the port incommunicable withthe pump outlet opening, a conduit leading from a 70 source of fluid tothe inlet opening, a valve in the conduit to control the pump inletpressure, a device to operate the valve, and a duct connecting theintermediate port and the device whereby saiddevice is actuated bypressure fluid at said port to operate said valve in accordance withvariations in the pump inlet pressure.

5. A vacuum pump having an inlet and outlet opening and an intermediateport incommunicable with the outlet opening, a. conduit leading from asource of fluid to the inlet opening, a valve in the conduit to controlthe admission oi. fluid to the inlet opening. a spring acting to openthe valve, a chamber having a diaphragm opposing the force of thespring, linkage connecting the diaphragm with the valve, and a ductconnecting the intermediate port and the chamber, whereby the diaphragmis actuated by pressure fluid at said port to operate said valve inaccordance with variations in the pump inlet pressure.

GEORGE H. WOODARD.

